Grid monitoring using synchrophasors

SIGUARD® PDP (Phasor Data Processor)

The load on electricity supply systems has increased continuously over the past few years. There are many reasons for this: Increased cross-border power trading in Europe, for example, is placing new demands on the tie lines between control areas. For example, power transmission on tie lines in the European grid increased almost 6-fold from 1975 to 2008 (source: Statistical Yearbook of the ENTSO-E 2008) Increased input of wind power and the planned shutdown of existing power plants will extend the transmission distances between generation and consumers. Severe weather and storms can put important lines out of operation, for a short time exposing the remaining grid to increased load quickly. This means that the power system is increasingly operated closer to its stability limit and new load flows arise that are unfamiliar to network control center operators. This is where SIGUARD® PDP (Phasor Data Processor) is of huge benefit. This system for network monitoring using synchrophasors helps with fast appraisal of the current system situation. Power swings and transients are indicated without delay to help the control center personnel find the causes and take countermeasures. Advantages for the user: SIGUARD® PDP, a fast monitoring system, detects the events and trends in grids with fluctuating load flows or highly loaded lines which conventional systems cannot detect at all or can detect too late. Detailed search of causes can take place after failures. Investment decisions for new equipment can be taken based on valid dynamic measurements. Protection settings can be checked and improved using the measured dynamic processes.

Grid monitoring using synchrophasors

Details

Choose whether you want to use SIGUARD PDP in the compact version “Substation PDC” as a communications machine or in its full user interface with the applications (“Enhanced PDC”). You can also select your own tailor-made solution from these product families. Three different SIGUARD PDP variants are available:

Version

MLFB body number

Description

SIGUARD PDP – Substation PDC

7KE6041

Low-cost PDC version, without operating station; no application such as e.g. island state detection possible. Use in the substation as data node for synchrophasor measured values.

SIGUARD PDP – Enhanced PDC

7KE6042

Full version including all options for connecting operating stations and using the applications

SIGUARD PDP – Functions upgrade

7KE6040

By upgrades, the desired options can exactly be added to a basic license or a pre-defined combination.

Functions

Synchrophasor Technology, PMU

Synchrophasors are vector measured values, that is, the magnitude and phase of the current and voltage are measured and transmitted. Applying a time stamp to the transmitted vector measured values allows a comparison of the measured values from different locations in the network. The figure shows how vector measured values are collected from different regions in the network and brought together at a central location.

To enable further processing of the information obtained from the synchrophasors, time stamping must be extremely precise. For that reason, the PMUs feature GPS-based time synchronization.

Current and voltage are supplied as a vector value with amplitude and phase

With these characteristics, the synchrophasors can provide a dynamic view in real-time of power swings and other phenomena in network operation.

Phasor Measurement Units (PMU)

A phasor measurement unit (PMU, figure 4) is a device for measuring and transmitting synchrophasors. The frequency and the frequency change (df/dt) are also detected. A PMU can be an independent device, or integrated in a protection unit, or in a fault recorder. For this purpose, Siemens offers the SIPROTEC 5 PMU, a fault recorder with integrated PMU functionality. The SIPROTEC 5 PMU (for instance, available in the bay control unit 6MD85) complies with the IEEE C37.118 (2011) standard which describes the communication protocol of the synchrophasors and the dynamic requirements of the PMU.

SIGUARD® Phasor Data Processing System

The SIGUARD® Phasor Data Processing (PDP) System has a modular structure and can be distributed over multiple computers. The system structure is shown in figure 5.

SIGUARD® PDP server

The central component of SIGUARD® PDP is the server. It is used both as the communication hub and the archive link. It also provides basic services such as system monitoring. The configuration can include multiple operator stations (SIGUARD® PDP UI), which can be remote from the server or operated on the same computer.

In a typical configuration, the server will run on a server computer with a backed-up power supply (UPS) while the operator station is located in an office environment or in the network control center.

SIGUARD® PDP UI operator station

The operator station is normally remote from the Phasor Data Concentrator. Multiple operator stations can be connected. On an operator station, the measured values can be viewed in online mode. In offline mode, significant events can be replayed for precise analysis. All windows run concurrently. Figures 6 and 7 show examples of the operator interface.

The operator interface can be quickly and simply adapted during operation. The power system status curve (upper portion of the screen) shows the weighted sum of the distances of all measured values from their limits, thus providing a view of the network status and the trend. If the curve exceeds the limit value, it will be colored red. Network areas that are in a critical state are displayed in the lower part of the screen in a geographic overview. Next to this is the work area in which phasor diagrams, time charts, and application curves (e.g. voltage stability curves) can be positioned. Further windows show the selection of measured values, pending messages, or the formula editor. The operator interface can be distributed over multiple screens, if necessary.

SIGUARD® PDP COM

This system module provides the communications link to the other PDCs. Again, protocol IEEE C37.118 is used. SIGUARD® PDP COM sends the configured data to up to five recipients at a settable transmission rate (frames per second). The transmission rates can be set separately and the measured values to be transmitted can be selected from all the available PMU measured values for each channel.

SIGUARD® PDP Engineer

SIGUARD® PDP Engineer is a user-friendly configuration tool for the entire SIGUARD® PDP system. The five work areas on the main screen clearly designate the task groups:

An integrated plausibility check ensures the consistency of the configuration.

Communication links

IEEE C37.118 server / client

OPC-to-OPC clients (application: automation functions)

ICCP (to network control Centers)

Applications

Analysis of the power flows in the system

SIGUARD® PDP can display a clear and up-to-date image of the current power flows in the system with just a few measured values from widely distributed phasormeasurement units (PMU). This requires no knowledge of the network topology. The power flows are shown by means of phase angle differences.

Monitoring of power swings

All measured values from PMUs can be displayed and monitored with easy-to-configure phasor diagrams and time charts. Any power swings that occur are quickly and reliably detected. The zone being monitored can be flexibly adjusted to the current situation in terms of time, geography, and content.

Evaluation of the damping of power swings

Using the function “Power Swing Recognition”, an incipient power swing is detected and the appropriate damping determined. Detection of a power swing and, if applicable, its insufficient or non-existent damping is signaled (alarm list).There are two ways of detecting a power swing: Based on angle differences between two voltages (two PMUs necessary) or based on power swing recognition of the active power (one PMU for current and voltage measured values is adequate).

Monitoring of the load on transmission corridors

The voltage-stability curve is especially suitable for displaying the instantaneous load on a transmission corridor. The currently measured operating point is shown on the work curve of the line (voltage as a function of the transmitted power). In this way, the remaining reserve can be shown at any time. This requires PMUs at both ends of the line.

Island state detection

This function automatically indicates if parts of the network become detached from the rest of the network. For this purpose, frequency differences and rates of frequency changes can be automatically monitored. If islands are detected, warnings and event messages are output. In addition, the islands are marked in the graphic overview as colored areas.

Retrospective event analysis

SIGUARD® PDP is ideal for analyzing critical events in the network. After switchover to offline mode, the entire archive can be systematically analyzed and the events played back as often as necessary. This makes dynamic events transparent, and reports can be quickly and precisely compiled. Simply copy the informative diagrams from SIGUARD® PDP into your reports.

Alarming on limit value violation with an alarm list and color change in the geographic network overview map This allows you to locate the position and cause of the disturbance quickly. This function is also available for analyzing the archive.

Display of the power system status as a characteristic value for the stability of the power system Due to the constant availability of the power system status curve in the upper part of the screen, the operator is constantly informed about trends in system dynamics and any remaining reserves. This curve shows a weighted average of the distances of all measured values, to their limit values.

Phase Angle Display

The Phase Angle Display Function can be activated in the geographic overview. It shows the voltage phase angle values between PMUs in a colored area. Together with the color scale for the voltage phase angles, the operator can check immediately the stability situation in the system. Colouring as well as min- and max-values can be set with the SIGUARD PDP Engineer.

Event-Triggered Archiving

Use SIGUARD PDP to automatically save recordings of abnormal system events. Define trigger events such as limit violations, recognized power swings etc. Select Lead Time and Follow-up time with SIGUARD PDP Engineer. The system then automatically saves all measurements in case the predefined event happens.

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